Investments In Fixed Maturity Securities Investments in Fixed Maturity Securities (Investments in fixed maturity securities) (Details) - USD ($)		Jun. 30, 2016		Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		$ 88,019,000		$ 96,267,000
Held to Maturity Securities Accumulated Unrecognized Holding Gain		21,758,000		18,453,000
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		109,777,000		114,720,000
Total held to maturity, Carrying Value		88,019,000		96,267,000
Total available for sale, Amortized Cost		12,311,389,000		12,012,041,000
Total available for sale, Gross Unrealized Gains		599,026,000		427,492,000
Total available for sale, Gross Unrealized Losses		(43,512,000)		(91,406,000)
Total available for sale, Fair Value		12,866,903,000		12,348,127,000
Total available for sale, Carrying Value		12,866,903,000		12,348,127,000
Total investments in fixed maturity securities, Amortized Value		12,399,408,000		12,108,308,000
Total investments in fixed maturity securities, Gross Unrealized Gains		620,784,000		445,945,000
Total investments in fixed maturity securities, Gross Unrealized Losses		(43,512,000)		(91,406,000)
Total investments in fixed maturity securities, Fair Value		12,976,680,000		12,462,847,000
Total investments in fixed maturity securities, Carrying Value		$ 12,954,922,000		12,444,394,000
Minimum ownership of Common stockholders equity		10.00%
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		$ 836,109,000		799,839,000
Total available for sale, Gross Unrealized Gains		66,413,000		50,310,000
Total available for sale, Gross Unrealized Losses		(4,183,000)		(12,689,000)
Total available for sale, Fair Value		898,339,000		837,460,000
Total available for sale, Carrying Value		898,339,000		837,460,000
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		97,524,000		64,975,000
Total available for sale, Gross Unrealized Gains		970,000		875,000
Total available for sale, Gross Unrealized Losses		(770,000)		(128,000)
Total available for sale, Fair Value		97,724,000		65,722,000
Total available for sale, Carrying Value		97,724,000		65,722,000
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		532,492,000		645,092,000
Total available for sale, Gross Unrealized Gains		28,680,000		27,660,000
Total available for sale, Gross Unrealized Losses		(682,000)		(2,333,000)
Total available for sale, Fair Value		560,490,000		670,419,000
Total available for sale, Carrying Value		560,490,000		670,419,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,595,942,000		2,510,816,000
Total available for sale, Gross Unrealized Gains		141,661,000		102,909,000
Total available for sale, Gross Unrealized Losses		(1,038,000)		(3,737,000)
Total available for sale, Fair Value		2,736,565,000		2,609,988,000
Total available for sale, Carrying Value		2,736,565,000		2,609,988,000
Corporation [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		387,006,000		388,904,000
Total available for sale, Gross Unrealized Gains		17,599,000		14,039,000
Total available for sale, Gross Unrealized Losses		(545,000)		(402,000)
Total available for sale, Fair Value		404,060,000		402,541,000
Total available for sale, Carrying Value		404,060,000		402,541,000
Debt, State Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		577,408,000		583,456,000
Total available for sale, Gross Unrealized Gains		35,119,000		28,068,000
Total available for sale, Gross Unrealized Losses		(987,000)		(2,070,000)
Total available for sale, Fair Value		611,540,000		609,454,000
Total available for sale, Carrying Value		611,540,000		609,454,000
Revenue Subject to Refund [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		448,185,000		439,772,000
Total available for sale, Gross Unrealized Gains		36,443,000		32,056,000
Total available for sale, Gross Unrealized Losses		0		(31,000)
Total available for sale, Fair Value		484,628,000		471,797,000
Total available for sale, Carrying Value		484,628,000		471,797,000
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost	[1]	1,010,596,000		1,126,382,000
Total available for sale, Gross Unrealized Gains	[1]	31,157,000		18,935,000
Total available for sale, Gross Unrealized Losses	[1]	(3,630,000)		(11,180,000)
Total available for sale, Fair Value		1,038,123,000	[1]	1,134,137,000
Total available for sale, Carrying Value	[1]	1,038,123,000		1,134,137,000
Non-credit portion of other-than-temporary impairments (OTTI)		985,213		1,269,491
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		3,562,935,000		3,403,953,000
Total available for sale, Gross Unrealized Gains		191,948,000		115,478,000
Total available for sale, Gross Unrealized Losses		(15,341,000)		(44,393,000)
Total available for sale, Fair Value		3,739,542,000		3,475,038,000
Total available for sale, Carrying Value		3,739,542,000		3,475,038,000
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		4,352,454,000		4,265,106,000
Total available for sale, Gross Unrealized Gains		266,525,000		201,342,000
Total available for sale, Gross Unrealized Losses		(2,570,000)		(6,269,000)
Total available for sale, Fair Value		4,616,409,000		4,460,179,000
Total available for sale, Carrying Value		4,616,409,000		4,460,179,000
Debt, Local Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		343,913,000		342,158,000
Total available for sale, Gross Unrealized Gains		35,703,000		24,270,000
Total available for sale, Gross Unrealized Losses		0		(29,000)
Total available for sale, Fair Value		379,616,000		366,399,000
Total available for sale, Carrying Value		379,616,000		366,399,000
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		1,108,120,000		1,191,357,000
Total available for sale, Gross Unrealized Gains		32,127,000		19,810,000
Total available for sale, Gross Unrealized Losses		(4,400,000)		(11,308,000)
Total available for sale, Fair Value		1,135,847,000		1,199,859,000
Total available for sale, Carrying Value		1,135,847,000		1,199,859,000
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		1,919,279,000		1,706,694,000
Total available for sale, Gross Unrealized Gains		13,333,000		12,892,000
Total available for sale, Gross Unrealized Losses		(16,336,000)		(14,414,000)
Total available for sale, Fair Value		1,916,276,000		1,705,172,000
Total available for sale, Carrying Value		1,916,276,000		1,705,172,000
Industrial Property [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,093,170,000		1,976,393,000
Total available for sale, Gross Unrealized Gains		128,048,000		75,168,000
Total available for sale, Gross Unrealized Losses		(6,795,000)		(30,027,000)
Total available for sale, Fair Value		2,214,423,000		2,021,534,000
Total available for sale, Carrying Value		2,214,423,000		2,021,534,000
Domestic Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		1,196,178,000		1,153,096,000
Total available for sale, Gross Unrealized Gains		50,925,000		31,744,000
Total available for sale, Gross Unrealized Losses		(7,565,000)		(11,819,000)
Total available for sale, Fair Value		1,239,538,000		1,173,021,000
Total available for sale, Carrying Value		1,239,538,000		1,173,021,000
Public Utility, Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		203,145,000		192,857,000
Total available for sale, Gross Unrealized Gains		12,391,000		8,321,000
Total available for sale, Gross Unrealized Losses		(972,000)		(2,527,000)
Total available for sale, Fair Value		214,564,000		198,651,000
Total available for sale, Carrying Value		214,564,000		198,651,000
Other Security Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		70,442,000		81,607,000
Total available for sale, Gross Unrealized Gains		584,000		245,000
Total available for sale, Gross Unrealized Losses		(9,000)		(20,000)
Total available for sale, Fair Value		71,017,000		81,832,000
Total available for sale, Carrying Value		71,017,000		81,832,000
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		70,704,000		77,129,000
Held to Maturity Securities Accumulated Unrecognized Holding Gain		19,312,000		(16,246,000)
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		90,016,000		93,375,000
Total held to maturity, Carrying Value		70,704,000		77,129,000
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		17,315,000		19,138,000
Held to Maturity Securities Accumulated Unrecognized Holding Gain		2,446,000		2,207,000
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		19,761,000		21,345,000
Total held to maturity, Carrying Value		$ 17,315,000		$ 19,138,000

[1] Gross unrealized losses for residential mortgage-backed securities include $985,213 and $1,269,491 as of June 30, 2016 and December 31, 2015, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income.